Method of drying pipe embedded in concrete



p 1 6 G. E. ZIEGLER 3,206,867

METHOD OF DRYING PIPE EMBEDDED IN CONCRETE Filed June 25, 1962 INVENTOR. 660776 5Z1? er I BY 7 l w Q A/TTORNEYS United States Patent 3,206,867 METHOD OF DRYING PIPE EMBEDDED IN CONCRETE George E. Ziegler, Evanston, Ill., assignor to Concrete Thermal Casings, Inc., Seattle, Wash, a corporation of Washington Filed June 25, 1962, Ser. No. 205,023 3 Claims. (CI. 34-22) The present invention relates to insulated pipe installations, including underground and overhead pipe installations, and a method of operating the same.

One particularly suitable type of installation for underground pipe systems involves the use of a relatively lightweight embedrnent of the type described in Goff, United States Patent No. 2,355,966. While installations embodying the Goff-type system have numerous advantages over other types of pipe embedment, such systems have the disadvantage of being rather permeable to moisture with the result that their insulating value decreases significantly whenever substantial amounts of moisture exist. Moisture vapor and liquid water may be present in insulation systems from various causes. Underground pipe installations may be damaged by improper backfill materials, or procedures, or by subsequent operations in the vicinity which cause a break in the waterproof casing materials which are commonly provided about the periphery of the pipe. In addition, if rupture of the pipe should occur due to improper welding or faulty pipe, the fluid from the pipe is likely to seep into the concrete casing.

Additionally, if the insulation is a hydraulically set concrete, a substantial excess of water is normally present in the concrete composition during its period of initial set. Unless the large excess of water is somehow removed, it remains to impair the insulating value of the concrete.

To overcome these difliculties, it has previously been suggested that the lightweight embedment be provided with vent passages within the body of the embedment extending in generally parallel relationship to the embedded pipe. The thermal gradient existing between the hot surface of the pipe and the cold surface of the embedment is sufficient to drive moisture vapor into the vent where it is carried off due to thermal siphoning, or by employing a positive displacement means such as a blower. Systems of this type are described in the copending application of Lincoln L. Loper, J12, Serial No. 9,036, filed February 16, 1960, now US. Patent No. 3,045,707 and in my copending application Serial No. 786,169, filed January 12, 1959, now US. Patent No. 3,045,708 of which this application is a continuation-inpart.

The addition of the vent passages substantially overcomes the moisture penetration problem under normal operating circumstances. The vents alone, however, are incapable of restoring the system to operating condition within a short time when the insulation is completely flooded, as may occur from a break in the pipe, or from flooding of a manhole. Some contractors require that any underground pipe insulation system should be in normal thermal efliciency operation 48 hours after the water has been drained. They further specify that the system in its operating condition must have a moisture content less than 5%. The rapid removal of such large amounts of water from the insulation, therefore, presents a significant problem which it is the purpose of the present invention to solve.

An object of the present invention is to provide an improved method for eliminating substantial amounts of water from an underground pipe installation in a short period of time.

A further object of the present invention is to provide an improved method for drying a pipe installation embedded within a relatively porous insulating mass.

Still another object of the invention is to provide an improved underground pipe installation with means for diffusing heated air through the insulation to remove water rapidly.

Still another object of the invention is to provide an improved composition suitable for use as a thermal insulating material in the types of pipe embedments with which the present invention is concerned.

One of the features of the present invention resides in providing an embedment of a relatively porous, insulating concrete having at least one vent passage extending in parallel spaced relation adjacent to the pipe and passing air under pressure radially outwardly from the outer periphery of the pipe while passing a heated fluid through the pipe. The thus heated air is then passed through the insulation at a mass velocity which is suflicient to force the moisture contained in the embedment into the vent passage for elimination from the system.

Other objects and features of the present invention will be apparent to those skilled in the art from the following detailed description of the attached sheet of drawings which illustrate a preferred embodiment of the invention.

In the drawings:

FIGURE 1 is a view in perspective partially broken away to illustrate one form of the present invention;

FIGURE 2 is a cross-sectional view of the pipe insulation system shown in FIGURE 1; and

FIGURE 3 is a cross-sectional view taken substantially along the line lII-III of FIGURE 2.

As shown in the drawings:

In FIGURE 1, reference numeral 10 indicates generally a poured structural concrete pad which rests upon the bottom of a trench dug for the purpose of accommodating a pipe line. A water impervious membrane 11 of generally U'shaped configuration is disposed over the pad 10, and a water impervious cover 12 overlaps the free ends of the membrane 11 as best illustrated in FIG- URE 3 of the drawings. The impervious casings 11 and 12 are not essential to the practice of this invention and may sometimes be eliminated.

In the particular installation shown in the drawings, there is provided a single fluid carrying pipe 14 although, obviously, any number of pipes can be included in the embedment. The pipe 14 is shown temporarily supported upon spaced support blocks 15 composed of a thermal insulating concrete mixture. While the particular embodiment of the invention illustrated in the drawings comprehends the use of such support blocks, it should be understood that the invention is equally applicable to installations in which the fluid carrying pipes are guided and supported by the insulating concrete, and to systems in which the pipes are guided and supported by means such as pipe guides, rollers, rockers and the like in which the insulation has primarily a thermal function.

The thermal insulation which provides the embedment for the pipe is illustrated generally at reference numeral 16 in the drawings. For the purposes of this invention, I prefer to use a new type of composition which will be described more specifically in a succeeding portion of this specification. For the present, it will be sufficient to say that the embedment 16 is relatively light weight and is relatively permeable to moisture. It may be hydraulically set, light Weight concrete, or a porous insulating material such as foamed plastic. It may be monolithic or sectional. To carry away moisture vapor which exists under normal operating conditions, the embedment is pro- 3 vided with spaced vent passages 17, 18, 19, and extending the full length of the embedment, and in generally parallel spaced relationship to the pipe 14. The vent passages 17-20 have been shown as cylindrical merely for convenience, as other geometric shapes will function as well. Furthermore, the number of vent passages can be larger or smaller than four, depending upon the particular installation. In fact the vent passages 17-20 may be eliminated entirely where, for example, the pipe is laid in porous soils without the impervious casings 11 and 12 so that the air and moisture can diffuse directly from the insulating concrete into the soil.

In accordance with the present invention, a substantial length of the pipe 14 is initially covered with a parting medium which may consist of convolutions 21 of a corrugated paper treated with asphalt or the like so that it is not softened by the light weight concrete embedment 16 which is poured around it. The parting medium 21 exists as an integral structure only until such time as the steam transmission through the pipe 14 commences, whereupon the asphalt is melted, and the paper charred, disintegrated, or at least rendered porous to air flow. The resultant artial or complete destruction of the parting medium thereby provides a plenum chamber for air between the hot, outer periphery of the pipe 14 and the embedment 16 which surrounds it.

Air, at a controlled velocity, is introduced into the resulting plenum chamber by means of a sleeve 22 which is positioned about a portion of the periphery of the pipe 14 and has a fitting 23 extending to an air supply (not shown) which directs the air along the sleeve and into the plenum chamber provided by the distintegration of the parting medium 21. Caulking material 24 is provided to seal off one end of the sleeve 22 to prevent air flow in the opposite direction. The plenum chamber 'need not surround the entire periphery of the pipe 14, and may be of various cross-sectional configurations and sizes, formed by any convenient method.

The air introduced through the inlet 23 is warmed by contact with the hot surface of the pipe 14, since the fluid in the pipe is normally at a temperature above the ambient temperature of the surroundings, and in a steam line will be above the boiling point of water. The air under a slight positive pressure then diffuses radially through the insulation and into the vent passages 17, 18, 19, and 20 from which the moisture laden air is removed. The removal of air and vapor from the vent passages can be increased by thermal siphon effects or by providing a positive displacement means such as a blower in communication with the vent passages.

The pressure differential between the Plenum chamber provided about the periphery of the pipe 14 and the vent passages 17, 18, 19, and 20 may not be very high, but I have found that a pressure difference of at least two inches of water gauge should be employed for practical drying rates. A pressure difference of 12 inches of water gauge between the air space in contact with the pipe and the vent passages is very acceptable for an installation in which there are four vents provided, one in each corner, where the pipe is at a temperature of about 350 F., and where the insulation thickness is about three inches.

The maximum pressure differential is determined by the fluid flow characteristics of the vent passages. Applied pressures in excess of about 125 pounds per square inch are not practical nor are they necessary to secure the improved results of the invention.

The air flow rate is the most important single factor in securing proper diffusion drying. Actually, with more porous concrete mixes, the air flow rate will be higher.

' Generally speaking, therefore, an air flow rate of 2 to 25 cubic feet per inch of insulation thickness per minute per inch of water pressure difference per square foot of insulation cross-section perpendicular to the direction of air flow will be appropriate.

The drying system of the present invention works particularly well with a new type of insulating concrete which forms another feature of the present invention. Heretofore, such insulating concrete made use of a waterproofing liquid emulsion which was difficult to work with and had to be protected from freezing in the field. The new composition provides a dry waterproofing pre-mix which can be added to the aggregate prior to combining the aggregate with Portland cement and water. Basically, the new composition consists of a mixture of an expanded aggregate (such as expanded vermiculite or perlite) coated with a thin film of a bituminous material and combined with a water insoluble stearate waterproofing agent, an air entraining agent and a metal passivator.

The coated aggregate is preferably of the type described in Sucetti, United States Patent No. 2,824,022, issued on February 18, 1958. The coated particles, as described in that patent, are produced by providing a moving bed of hot particles of aggregate and applying to the moving bed an aqueous dispersion of a bituminous material. The water contained in the dispersion is volatilized by the sensible heat of the particles to effect a steam dispersion of the water resistant material throughout the bed. Each particle is thereupon coated with a continuous uniformly thin film of water resistant material of a thickness less than about 10 microns, the particles being noncoalescing and having a substantially reduced capillary uptake capacity.

The water insoluble stearate is preferably calcium stearate but may consist of aluminum stearate or zinc stearate. Generally, at least 0.1 pound of the stearate should be added for every cubic foot of the aggregate. At quantities greater than about 0.5 pound of stearate, there is little additional benefit to be derived, and the cost becomes prohibitive.

The air entraining agent can be any surface active material which is normally used to entrain air in aqueous systems, but I prefer to use a material such as Hercules NV because this material provides a particularly strong or permanent bubble structure when present in the wet, insulating, concrete mass and also provides some water proofing effect of its own. Hercules NVX is a neutralized Vinsol resin, the latter being a mixture of resinous materials recovered as a black residue after the extraction of rosin with petroleum solvents. In a typical process for the recovery of the resin, pine wood is extracted with a hydrocarbon solvent such as benzene to extract materials such as turpentine, pine oil, rosin, and the aforementioned residue. Subsequently, the turpentime and the pine oil are distilled off and the remaining materials are extracted with a petroleum derivative such as petroleum ether. After removal of excess solvent, the dark colored resinous substance is recovered. The

I preferred range for the air entraining agent is from 0.01

to 0.2 pounds of the agent per cubic foot of micaceous aggregate.

A passivator is added to lower the electromotive force which is inherently present between the metal pipe and its environment, which electromotive force could cause electrolytic corrosion. Sodium nitrite is particularly preferred for this use, but potassium or sodium dichromate can also be substituted but with less effective results. Sodium nitrite should be added in quantities of at least 0.04 pound per cubic foot of the aggregate. Quantities in excess of about 0.3 pound per cubic foot are not necessary and render the cost prohibitive.

While not necessary for the purposes of the invention, it is desirably to add to the pre-mix composition a small amount of expanded vermiculite. This material is added for convenience in manufacturing and handling since it improves the physical mixing characteristics. Quantities of less than about 0.04 pound percubic foot of the coated vermiculite do not provide significant improvement, and quantities greater than about 0.4 pound per cubic foot of the coated aggregate are undesirable because they add bulk to the mixture that increases handling and transportation costs.

The waterproofing pre-mix, containing the stearate, air entraining agent, and passivating agent is added to the coated aggregate particles (usually having a density of 6 to 8 pounds per cubic foot) in a ratio of about 2 pounds of the dry powder to 3 cubic feet of the coated vermiculite aggregate. The resulting mixture is then combined with Portland cement and water in the normal ratios for making light weight concrete, that is one bag of Portland cement (94 pounds) to 4 to 10 cubic feet of the pre-mix.

A test installation including a centrally disposed steam pipe and four vent passages of the type shown in the drawings was tested by thorough immersion in water for a period of about 72 hours. The insulation was then dried by maintaining a steam pressure of 125 pounds per square inch gauge in the pipe, and venting the vent passages to the atmosphere, while introducing air into the sleeve provided for that purpose. The ventilating air pressure as measured in the plenum chamber was maintained near 12 inches of water gauge. The air flow in the vent passages was measured by means of an anemometer. The maximum velocity in the two lower vent tubes was 455 feet per minute, and in the two other tubes was 425 feet per minute. After 48 hours drying, the casing on the conduit was carefully removed and residual moisture tests were made. Circumferential samples were taken and dried in an oven at 220 F. Samples near the low end of the insulation evidenced a moisture content of 3.1%, while those that were taken from the center and near the high end of the insulation evidenced only 1.3% moisture.

It should be evident that various modifications can be made to the described embodiments without departing from the scope of the present invention.

I claim as my invention:

1. The method of drying a pipe installation in which said pipe is surrounded by a relatively porous embedment of insulating concrete having at least one vent passage extending the full length of the embedment and in parallel spaced relation to said pipe which comprises establishing an air pressure differential of at least two inches of water between the outer periphery of said pipe and said vent passage by passing air under said pressure differential radially outwardly of the outer periphery of the pipe through the embedment and into said vent passage, passing a heated fluid at a temperature above the boiling point of water through said pipe, and continuing the passage of air through said embedment and into said vent passage until the moisture content of said embedment is substantially reduced.

2. The method of drying a pipe installation in which said pipe is surrounded by a relatively porous embedment of insulating concrete having at least one vent passage extending the full length of the embedment and in parallel spaced relation to said pipe which comprises establishing an air pressure differential of at least two inches of water between the outer periphery of said pipe and said vent passage, passing a heated fluid at a temperature above the boiling point of water through said pipe, and passing air at mass velocity of at least two cubic feet per inch per minute per inch of water pressure differential per square foot radially outwardly from the outer periphery of said pipe through said embedment and into said vent passage until the moisture content of said embedment is substantially reduced.

3. The method of claim 1 in which said embedment comprises an insulating concrete containing Portland cement and expanded vermiculite.

References Cited by the Examiner UNITED STATES PATENTS 182,426 9/76 Everett 34-22 1,184,472 5/16 Medway 138-106 1,991,455 2/35 Gottwald 138106 2,555,587 6/51 Fisher 34-22 2,598,981 6/52 Denning 106 88 2,614,939 10/52 Keating 106-88 2,707,984 5/55 Goff 138'106X 2,721,468 10/55 Pole 34 104 2,969,027 1/61 Figge 34-104 3,032,827 5/62 'Schaifer 138-106 3,045,707 7/62 Loper 138--106 3,045,708 7/62 Ziegler 138- 106 NORMAN YUDKOFF, Primary Examiner. EDWARD V. BENHAM, Examiner, 

1. THE METHOD OF DRYING A PIPE INSTALLATION IN WHICH SAID PIPE IS SURROUNDED BY A RELATIVELY POROUS EMBEDMENT OF INSULATING CONCRETE HAVING AT LEAST ONE VENT PASSAGE EXTENDING THE FULL LENGTH OF THE EMBEDMENT AND IN PARALLEL SPACED RELATION TO SAID PIPE WHICH COMPRISED ESTABLISHING AN AIR PRESSURE DIFFERENTIAL OF AT LEAST TWO INCHES OF WATER BETWEEN THE OUTER PERPHERY OF SAID PIPE AND SAID VENT PASSAGE BY PASSING AIR UNDER SAID PRESSURE DIFFERENTIAL RADIALLY OUTWARDLY OF THE OUTER PERIPHERY OF THE PIPE THROUGH THE EMBEDMENT AND INTO SAID VENT PASSAGE, PASSING A HEATED FLUID AT A TEMPERATURE ABOVE THE BOILING POINT OF WATER THROUGH SAID PIPE, AND CONTINUING THE PASSAGE OF AIR THROUGH SAID EMBEDMENT AND INTO SAID VENT PASSAGE UNTIL THE MOISTURE CONTENT OF SAID EMBEDMENT IS SUBSTANTIALLY REDUCED. 